Advanced Research Projects Agency
(ARPA) Established in 1958 "for the direction or performance of such advanced projects in the field of research and development as the Secretary of Defense shall, from time to time, designate by individual project or by category." The name ARPA was used from 1958 to 1972 and from 1993 to 1996. Otherwise known as Defense Advanced Research Projects Agency (DARPA).

Source:
http://www.darpa.mil/body/arpa_darpa.html